(1) Field of the Invention
This invention relates to novel compounds of 1,2-di(4-isobutylphenyl)ethylene and 1,2-di(4-isobutylphenyl)ethane.
These novel compounds can be used as intermediate materials for preparing inexpensively and economically .alpha.-(4-isobutylphenyl)propionic acid (tradename: "Ibuprofen") which is useful as a medicine for the relief of fever, pain and inflammation.
Furthermore, the invention also relates to a method for producing ibuprofen through 4-isobutylstyrene from the above novel compounds.
(2) Description of the Prior Art
.alpha.-(4-isobutylphenyl)propionic acid is an excellent medicine because it is effectual in the relief of fever, pain and inflammation and it has little side effect. Therefore, various kinds of synthesis methods have been proposed. One of them, it is proposed to prepare the medicine from 4-isobutylstyrene through hydroformylation or Reppe process. More particularly, the method is proposed in, for example, British Patent No. 1,565,235 and U.S. Pat. No. 4,694,100.
This method using 4-isobutylstyrene is one of economically advantageous methods because 4-isobutylstyrene is a simple and stable substance and the hydroformylation and Reppe process do not require any expensive reagent.
As a method for producing alkylstyrenes, the catalytic cracking of 1,1-diarylethane is hitherto proposed. For instance, in the specification of the foregoing U.S. Pat. No. 4,694,100, a method for preparing 4-isobutylstyrene is disclosed in which method 1,1-di(4-isobutylphenyl)ethane is catalytically cracked. In the same patent specification, the method for preparing ibuprofen by hydroesterification or hydroformylation of 4-isobutylstyrene is also disclosed.
In this method, however, it cannot be avoided that an equimolar amount of isobutylbenzene is theoretically produced simultaneously with the formation of the aimed 4-isobutylstyrene. Accordingly, it has been necessary that this isobutylbenzene as a by-product is converted again into the starting material to be cracked.
Nevertheless, it has been found out that 4-isobutylstyrene can be obtained without the formation of the by-product, isobutylbenzene, by subjecting 1,2-di(4-isobutylphenyl)ethylene of the present invention to disproportionation with ethylene.
In addition, the above catalytic cracking of 1,1-di(isobutylphenyl)ethane has another disadvantage. That is, in the catalytic cracking as disclosed in the above references, not all of the starting material is cracked and it cannot be avoided that unreacted starting material remains in the reaction mixture. This is apparent from the fact that the purpose conversion rates in the method proposed above are from 40% to 60%.
In order to produce economically alkylstyrene by cracking, the reuse of the unreacted 1,1-di(substituted phenyl)ethane is inevitable. In other words, it is an inevitable condition for economizing the industrial practice of cracking reaction that the fraction mainly containing 1,1-di(substituted phenyl)ethane that is separated from a reaction mixture is used again for a cracking step.
The inventors of the present invention have made extensive investigation with regard to the preparation of alkylstyrene by cracking. As a result, it was found out that, in the conventional method for cracking 1,1-di(substituted phenyl)ethane, the properties of the fraction mainly containing 1,1-di(substituted phenyl)ethane is not suitable for use again in cracking, because ethylene components are contained; and that, when the new compound of 1,2-di(substituted phenyl)ethane is used as a material to be cracked, the formation of such ethylene components is not observed and any problem is not caused to occur even when the fraction containing unreacted material is used again. That is, in the cracking of 1,1-di(4-isobutylphenyl)ethane in the conventional art, ethylene components which are formed by dehydrogenation with a cracking catalyst are contained in the fraction of unreacted material as shown by the following chemical equation. In addition, these ethylene components are hardly separated by distillation because they have close boiling points. When the cracking of unreacted 1,1-di(4isobutylphenyl)ethane fraction containing ethylene components is carried out, the life of cracking catalyst is affected adversely. EQU Ar--CH(--CH.sub.3)--Ar.fwdarw.Ar--C(.dbd.CH.sub.2)--Ar
wherein Ar is an aryl group.
In connection with the new compound, 1,2-di(4-isobutylphenyl)ethane of the present invention, the formation of ethylene components can be avoided and the reuse of the fraction containing unreacted material does not affect adversely on the life of cracking catalyst, therefore, the efficient production of 4-isobutylstyrene could be first accomplished by this invention.